1. Field of the Invention
The present disclosure relates to mitigating the adverse effects of inter-symbol interference (ISI) at the receiver of a network system such as, for example, an Orthogonal Frequency Division Multiplexing (OFDM) system. The present disclosure also relates to reducing the amount of time required by a receiver to complete the initial synchronization procedure and cell search procedure.
2. Background Art
In OFDM systems using wireless channels, when a data signal is transmitted over a wireless channel, the signal can be distorted due to multipath. Multipath occurs when the transmitted signal travels over multiple paths, and the multiple signals reach the receiver at different times depending on the distances traveled along the respective multiple paths. The distances traveled along the respective multiple paths are different because some paths are more direct than others. As such, the same signal travels over multiple paths and reaches the receiver at different times. As explained below, the delays between the different times at which the same signal is received at the receiver causes ISI.
The data included in the signal is organized in frames which contain a plurality of symbols. ISI can occur when the same symbol is received at different times due to channel multipath, and therefore may interfere with an adjacent symbol, causing bit errors.
Channel estimation is a process used to estimate the frequency and spatial response of a channel or the path between a transmitter and receiver, and is used to configure receiver parameters (e.g. gain control, equalizer parameters, and the like). One or more pilot signals may be sent from transmitter and receiver, where the pilot signals are previously known to the receiver. Upon reception of the transmitted signal, the receiver compares the received pilot information to the known pilot information and derives the channel estimate based on the results of the comparison. The pilot signals may be interspersed with the data signals to periodically perform the channel estimate during data transmission. Similar to the actual data signals, ISI also has a deleterious effect on pilot reception and therefore channel estimation. Further, since channel estimation is used to configure receiver parameters, any ISI effects on pilot reception has an even greater effect on future data signal reception and bit error rate (BER).
Therefore, there is a need to mitigate the effects of ISI on the accuracy of the channel estimation process.